Fluid motor



yMarch 17, 1953 o, E, DEMPSEY 2,631,572

FLUID MOTOR OE. De. mpsey BY C .YW f" 0 March 17, 1953 o. E. Dl-:MPsEY 2,631,572

FLUID MOTOR Filed July 30, 1947 3 Sheets-Sheet 2 o a6 a x l a amA 71a 7s a B6 t: Y

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FIGB QE. Dempsey BY M March 17, 1953 o. E. DEMPSEY FLUID MOTOR Filed July 50, 1947 3 Sheets-Sheet 3 I /ea OLE: Dempsev C. www@ Patented Mar. 17, 1953 UNITED STATES PATENT OFFICE FLUID MOTOR Oscar E. Dempsey, Tulsa, Okla., assignor, by mesneassgnmenta to Byron JacksonCo., vLos Angeles, Calif., a corporation of Delaware Application July 30, 1947, Serial No. 764,668

(Cl. LZ1- 123) 'by way of limitation to a-fluid actuated lmotor plunger unit rand the control valve mechanism therefor.

It is an important object of this invention to provide a fluid actuated motor adapted to providea positive working stroke for utilization in numerous types of reciprocating piston apparatus.

And still another object of this invention is to provide a Vhydraulic piston impact unit having a pilot valve responsive to movement of the piston unit for controllingzthe position of a main valve which in turn controls thesupply pressure fluid for actuating the piston unit.

still another object of this inv'ention is to Vprovide a hydraulic plunger unit having a valve control mechanism which includes a pilot ,valve controlling the position of the main valve vwherein said pilot valve is always moved or pushed into or against a high pressure condition ,regardless of its direction vof movement.

And still another V4object vof this invention is to provide a ,hydraulic plunger unit having an -indepenolent valve control mechanism regulating the .stroke of the plunger s o that on the working stroke of thev plunger, the exhaust pressure is substantially eliminated thereby providing va more positive and efficient working lstreke for the hydraulically actuated plunger .unit

vAnd still another Aobject of this invention is to provide a hydraulic vplunger unit where the input pressure is constantly maintained on one face of the plunger, and regulated or controlled pressure is directed to the v opposite face of the plunger to cause a working strokeithereof.

And still another object of this invention is to provide a hydraulic plunger unit having an independent valve control mechanism regulat- A:ing the stroke of the plunger and which includes a pilot valve movable'into a position to cause an exahust of vthe pressure fluid actuat- :ing the plunger prior tothe completion of the working stroke of the plunger'.

And still another object of this invention is to provide a fluid actuated piston unit incorporating a component valve mechanism therein. comprising a main and pilot valve assembly so arranged that the powerviiuid consumed on the piston lback stroke transfers to the power stroke cavity of the piston cylinder withouthim rdrance from exterior environment, thus allow- .ing the finiti .power to ir'nplement the forward stroke in an unrestricted thrust against Ythe piston.

And still another object of this invention is to provide a uid vactuated motor so devised that the piston moves through its forward or power stroke without spent or exhausting power fluid leaving the piston cylinder, andalso wherein the combined vfluid Adisplacement of va complete piston cycle exhausts during the sequent reverse or back stroke thereof.

An additional object of this invention is Vto provide a hydraulic piston body having -two working faces of selective cross-sectional area wherein the constantly maintained input -pressure against one face is sufcientfto -causereverse or backward power movement of the piston body while effecting the manageable exhaust of fluid responsible rfor a previous piston cycle into an environment of variable pressure, and wherein the cross-sectional area of the second face may be proportionately small so that the power fluid implementing the reverse stroke constitutes the major portion of the fluid movement toward the second face to effectively snub excessive forward piston ,speed` Other objects and advantages of theinvention will be evident from the following detailed description read in conjunction with the accompanying drawings which illustrate my invention.

In the drawings:

Figure 1 is a vertically sectional view of the Working parts of the invention, and showing one position of the valve control mechanism and the piston unit.

Figure 2 is a vertically elevational view vwith certain parts in section disclosing the invention adapted for use with an impact punch.

Figure 3 is a view similar to Figure Y'1 showing another position of the valve control mechanism and piston unit.

Figure 4 is a similar view to Figure `l `and showing still another position of Athe working parts.

Figure 5 is a vertically sectional view with certain parts in elevation showing the invention utilized in the oil well pump.

Figure 6 is a schematic view of the valve v and piston mechanism of the unit shown in Figure.

Referring to the drawings in detail, and more particularly Figures l and 2, the piston unit comprises anouter sectional 'housing generally indicated at 2, having an upper sleeve i Vand a lower sleeve 6. An adaptation of the valve and piston unit is disclosed in VFigure 2, and relates -to a road punch or horizontal digger generally indicated at 3, and comprising an outer shell having a plurality of spaced brackets l supporting the outer housing 2 of the valve unit disclosed in Figure 1. It will be understood that although the invention is preferably shown with a horizontal ditch cutter, that the application or utilization of the apparatus is not limited thereto. rihe further adaptation of the piston and valve unit to the road punch 3 will be hereinafter set forth.

Referring to Figure 1 and the working parts of the plunger unit and its co-operatng valve control mechanism, the upper cylinder 4 is provided with an end plate 3 welded thereto at Hi. The end plate 8 is providedwith a sleeve I2 extended therethrough by threading into an aperture I4 in the plate 8. A pipe or sleeve l5 is welded at I8 to the upper face of the end plate B and, in turn, is adapted to receive a supply pressure conduit l2 secured thereto. The upper end of the tube l2 receives a cap 25 threaded thereto. The upper housing 4 is secured by threading (not shown) at 2| to the lower housing 5. The lower housing 6 receives angled spacer plate 22 welded thereto and, in turn, having a pipe 23 of smaller diameter welded thereto. A 'nut 24 is threaded to the pipe 23 for holding packing 25 between the pipes 23 and 35 for a purpose as will be hereinafter set forth. A ring 25 is welded to the inner periphery of the cylinder 5 for supporting a plurality of packing rings 2l for a purpose as will be hereinafter set forth.

A piston generally indicated at 28 is disposed in the housing 2, and comprises an outer cylinder 29 and inner cylinder 3B spaced therefrom. The cylinders 29 and 35 are secured together at their upper end by a spacer ring 3| welded thereto, and at their lower end by a welded spacer ring 32. It will be noted that the outer cylinder 25 extends vertically only a portion of the length of the inner cylinder 30, particularly at the location of the spacer ring 32. However, the inner cylinder 3B extends below the spacer ring 32 and outside of the housing cylinder B. Leakage is prevented by the packing 25. It will be apparent that the retaining nut 2@ and spacer 22 holds the packing as well as the piston bearing sleeve 33 in the space between the cylinder 35 and the short cylinder 23. A ring 34, preferably of rubber or resilient material, is disposed immediately above the spacer 22 and within the housing cylinder 6. This circular ring acts as a bumper and particularly for the spacer ring 32 as will be hereinafter set forth.

At a point adjacent the spacer ring 32 the inner cylinder is provided with a plate or baiiie 35 welded to the inner periphery thereof. The plate 35 is provided with a central bore 35 into which is threaded a tube 3l extending downwardly therefrom. A horizontal bore 33 provides communication with an aperture 39 in the cylinder 3B thereby providing communication with the chamber 44 between cylinders 25 and 3G, and the aperture 35 in the plate 35. It will also be apparent that the outer cylinder 29 is provided with an orifice or aperture es providing communication between the chamber 42 and a chamber 4| between the cylinder 35 and the cylinder1 5. The outer housing is provided with an aperture 42 adapted to communicate with an outlet aperture 43 in tube l5 by any conventional conduit 43a (Fig. 2). The piston unit 28 is adapted to receive an internal valve unit generally indicated at 45.

The valve unit comprises a housing 4E havinga cylinder 4l secured thereto and extending upwardly therefrom to receive a threaded nut 48 which, in turn, is threaded to a cylinder 49 extending upwardly into welded contact with an apertured plate threaded to the piston cylinder 35. The housing 46 is provided with a central bore 5| having vertically spaced counterbores 52 and 54. An apertured valve seat 53 is pressed into the bore 5|. At a point adjacent to counterbore 54 the main bore 5| is provided with an apertured spacer ring 56 pressed therein. Immediately above the spacer ring 55 is provided a second apertured valve seat 57 arranged in inverted position relative to the valve seat 53 as will be hereinafter set forth. The spacer ring 55 is provided with transverse apertures 5B in alignment with the counterbore 54. It will be noted that the upper valve seat 5l' is provided with a central aperture 59 of variable diameters, and is arranged in a substantially convex position. The lower valve seat 53 is provided with a central aperture 59a of variable diameters, but arranged in a concave position. A vertically disposed cylinder 60 is pressed in the bore 5|, and is closed at its upper end with a plate 6| threaded thereinto. Encased in the cylinder 69 is the main valve generally indicated at 52. A vertical passageway 63 in the housing d5 provides communication between the countei-bores 52 and 54. The counterbore 52 also communicates with the chamber 64 provided between the cylinders 41 and 69.

The valve 52 freely disposed in cylinder B comprises a cylinder or sleeve 62a having a central bore 55 extending longitudinally through a portion thereof. The lowermost end of the valve 54. is provided with an aperture 56 into which is secured an extension valve 6l having an outer periphery of varying diameters adapted to cooperate with the apertured valve seats 53 and 51, as will be hereinafter set forth. The valve 5'! is provided with an axial bore 68. The aperture 56 communicates with drilled passageways 59 in valve 62, which in turn communicate with the central bore 55. Furthermore, the valve cylinder 62a is provided with drilled transverse exhaust passageways 'I0 providing communication between the bore 65 and the space il between the outer periphery of the valve sleeve 62a and the cylinder 55.

A pilot valve is loosely disposed in the bore 35 of the main valve E2 and comprises a sleeve l2 loosely disposed on an inverted T-shaped rod 13. The rod 'I3 is secured to a yoke connection 'f4 disposed in the bore 65 above the valve sleeve l2. The loose disposition of the sleeve 12 on the rod 73 is such to provide a passageway 'i5 providing communication from the lower side cf the valve sleeve 'I2 to the upper side thereof. The yoke i4 has a leg portion 16 extending vertically upward through a bushing 'il provided in the apertured plate 5|. The leg 16 is coupled by nut Tia with a valve rod l5. The valve rod 'I8 extends upwardly into the sleeve i2 and through a bushing i9 moveable within the sleeve l2. The

bushing also anchors one end of a helical spring S8 disposed in the sleeve l2 between the bushing i9 and a lower bushing '19a disposed adjacent the apertured lower end 8l thereof. The end 8| of the sleeve i2 is apertured to permit extension of the shaft or valve rod 'I8 therethrough into the connection with the nut Ta. The upper end of the shaft 18 receives a nut 82 for a purpose as will be hereinafter set forth. The inner periphery of the sleeve I2 is provided with in- 7 S above the piston unit 28 and thus repeating the working stroke of the piston unit 28;

It will be apparent that the spring functions to cause movement of the pilot valve before the piston unit 28 completes its full working stroke, however the momentum of the piston actuated by the supply pressure uid will permit the piston to move through a complete working stroke into contact with the rubber bumper 34 as will be hereinafter set forth.

From the foregoing it will be apparent that the pilot valve 'l2 is caused to be moved by a motivation of the main piston which motivation is controlled by the pilot valve determining the position of the main valve 52 which controls the supply pressure uid.

Movement `of the piston unit 23 moves the pilot valve '12, movement of the pilot valve 'l2 controls the position of the main valve 52, and the position of the main valve 62 controls the supply pressure iiuid for moving the piston 28 in one of two directions.

It will also be apparent that the pilot valve rod is always moving into or pushed into or against a high pressure area regardless of the direction of movement of the piston unit 28, and consequently away from a low pressure area. Furthermore, the pilot valve 'i2 is always moved in a direction opposite the next desired movement of the main valve 62. The particular operation of the pilot valve is such that the piston unit is provided with a reciprocating stroke without regard to the velocity of the stroke, rhythm or momentum. rThe positive action of the pilot valve is such that it does not have any on-center position and its movement is highly sensitive to any changes in pressure conditions on either side or the piston unit causing movement thereof.

The application of the valve and kpiston unit with a road punch or impact tool (Fig. 2) utilisos a ram, such as an extension pipe Si coupled to the piston cylinder 3@ by any conventional coupling means SS. A circular cutter head il@ is secured to the end of the ram Q1 by cross bars iill secured to a nut lili. Clamp members it 'co-operate with the brackets i for maintaining the housing unit 2 in the cylindrical sleeve 5.

it will be apparent that the piston unit d disclosed in Figures l, 3 and s in a movement toward the ring causes a [power stroke of the ram Si, and its complementary cutter E9. Furthermore, the valve unit 52 and pilot valve l2 control the supply pressure iiuid to permit a reversal of the piston unit Zitto move the ram 9i and cutter ils in a direction. toward the ring i, where again the piston unit E8 is in position to provide a working stroke to the cutter 85'. The horizont-a road punch is particularly adapted as auxiliary apparatus utilized. in the laying or" pipe line across the country. Many difficulties have been experiin providing a ditch for the pipe underneath paved roadways, streams, canals and the like. The road punch may be placed contermi- `ous with the pipe line ditch and actuated to Ylill or bore an aperture under a roadway necessary to lay a pipe line therethrough. The movement of the shell 5 longitudinally in the boring opere-.tion is controlled by any conventional mechanism (not shown). It will be apparent that the cuttings from the circular cutter 99 are pushed or moved into the interior of the cylindrical shell i during the operation 0i the ram Si. As the shell 5 is lled with the earth cuttings, the apparatus is removed and dumped, where it is again disposed in the bore to continue the cutting or boring operation.

The action of the spring to move the pilot valve and cause a movement vof the main valve 62 prior to the completion of the stroke of the piston unit is particularly advantageous in the road punch, shown in Figure 2, particularly where the boring operation is only through dirt and the like. The momentum of the piston is such to move it through its complete stroke after reversal of the valve l2, in boring through the earth, and thus provide an additional boring action for the piston. However where the cutter is contacting shale, hard rock and other material difficult to penetrate, the additional boringraction by the momentum of the piston is not present, and the action of the spring changing the position of the pilot valve wil1 provide an immediate retrograde action of the piston unit 28 in order to :provide successive impact strokes against the hard shale or the like.

Figures 5 and 6 disclose a modified adaptation of the valve and piston unit shown in the pre fel-red embodiment, as a vertical reciprocating.

unit for use in a bottom hole oil well pump. The mechanism in this adaptation is shown disclosed in a tubing string |93 disposed in spaced relation to the well casing Idil. The tubing string is provided with inwardly projecting shoulders $65 for supporting the pump housing generally indicated at i. The lower end of the string |533 is of reduced diameter as at IQ? for receiving the lower end 1&8 of the unit it, supported therein by packing cups H39. A plurality `of circumferentially spaced inlet apertures El] are provided in the reduced portion iil'l'. The pump unit IGS connects with a string of macaroni tubing ii extending from the well surface .for supplying the motive .pressure fluid from a source (not shown) as will be hereinafter set forth. The valve and piston mechanism of the preferred ernbodiment is utilized as the bottom hole pump ist, however the structure is arranged as shown in the schematic drawing of Figure 6. In this adaptation the main valve S2 of the preferred embodiment is shown disposed in an inverted position relative to Fig. l with the extension valve el and pilot valve l2 likewise inverted. The pist-on unit 23 of the preferred. embodiment has been modied and is disposed in the lower housing portions H2 and H3 of the ypump unit |56.

Referring to the Figure 6, the modified piston unit ||4 comprises a cylindrical piston ||5 having an enlarged head or fiange ||6 at one end, and a similar enlarged head ||7 at the opposite end. The piston heads IIS and Il? are provided with packing rings IIB. rThe valve rod 'I8 of the preferred embodiment extends through an'aperture ||9 of the upper flange I6. The lower piston head lll has an aperture |2|i. A ball valve |20a is disposed above the aperture ||9 acting as the valve seat. A port |2| is provided in the head I for a purpose as will be hereinafter set forth.

In the schematic showing of Figure 6 the supply pressure fluid from the tubing is directed through a passageway |22 irl-housing |66 to a chamber |23 beneath the underface of the upper piston ange I6.

In the position shown in Figure 6, the piston has completed its working stroke, and has started the upward or exhaust stroke. The supply pressure uid in chamber |23 will react against the difference in cross-sectional area between the packing ring ||8 and the packing gland |24 to cause upward movement of piston unit I4 as eX- haust supply iiuid leaves chamber 8s, which simultaneously moves lower piston head Ill upward to displace any well uid present in av chamrthe head H6 into engagement with,l the coupling nut '11a connected with the valvel 'I2 to cause movement of the nut Tia. inthe same direction thereof with al simultaneous. movement ofY the valve 12 tocloserof the passageways. B9 and the chamber 96 fromsupply pressure fluid, and uncover the exhaust passageways 'l0 in communication with the exhaust passagewaysf 81 and 88, thereby relieving the-pressure in chamber |30on one side of thezmain valveI 5.2. This positionof valve '|2directs the supply; pressure fluid in passageways |3.| againstzfthe valve-V61 tomove the valve B1, and the connectingmainyalve; t2 in a direction toward the pistonA unit; ||4 thereby opening theinlet port 51e; andpassageway to supply; pressure iluid.

Supply pressure viiuid isthen directed into the chamber 8S` toinuenceonefaceof piston ange l lr6 and*V cause movement;v of; the piston I I5` inY a direction towards; the( standing valve |21v in a working stroke. The downward .or working stroke of; the'V piston unit H4;displaceszproduction fluid that mayfbe present; inchamber |29, through the valve |20, orice |2| and-into thechamber |25, which fluidv is': partially, displaced ony the downward movement ofrthe piston I l;

Continued downward; movement of the piston unit will engageange- H5 with the nut 82 to positively move the valvev 'l2 simultaneously therewith. Downvtard.movementA of the Valve 12 with blocken; exhaust portsl and permit now of supply pressurefluidv throughfpassageways 68 and passageway 'l5v intothe chamber |30. As. soon as the supply pressure vin chamber |30 is increased, it will move the main valve1unit`62 ;and extension valve 6.1 into aseating,positionV asshcwn in Figure .andrclose oi the-,supply pressure fluid from orificev 54 and chamber 86: The supplypressure fluid is-constantly maintained through passagewayv |22' tothe chamber- |23, theninfiuences :the underface of: flange 6 :andgmoves the piston unit upwardlyin a'repeated-operations The displacement of- Iiuid into the. reservoir chamber '|2 6 constantly; creates an: increase in the hydrostatic head: therein, which when suiiicientlyl high will causeactuationot a differential valveunit |32 similar'tofthat of applicants copending application, Serialy No. 690,006, filed August; 6. 19.46,- now Ratent No.- 2,50,1,380,iissued March 21,1950, todirectflow'of supply pressure from the tubing through passageway |33 f ,or` slugging the liuid' inthe reservoir 26 to the surface of the fwell.

Fromr theY foregoing;v it will be apparent that thel presentv invention contemplates, ahydraulic power apparatus-i that' can be utilizedy .for various purposes. The apparatuscontemplates a; reciprocating; pistonV unit; having; a positive and emcient working; stroke., by, theA substantial elimination-of exhaust' pressure; againstthe working strokewhicnpermits thefpiston to-Ymovein a powerY stroke,` asexpeditiously as the regulated supply pressure iluid. is'` directed thereto. Furthermore thevalve: mechanismgand particularly the action of-the pilot valveeisfsuch that it moves against the pressure of; supply pressure -luid at all times, inv-orderv tvrllefmitivariable; positioningv or the; main va1ve-z for; controlling; or; regulating theflowof the supply vpressure fluid tothe power face of the piston unit.` Any pre-determined cushioning of the return or exhaust stroke of the piston unit may be controlled through the size of the exhaust ports which has thel particular advantage of either speeding up or slowing down the back ory return stroke ofthe piston for. various purposes. The hydraulic power apparatus may be modied tovarious-adaptation, as shown, such as a horizontal road punch or a bottom hole oil well pump without any substantial mcdication of the apparatus and particularly the operation of the valve mechanism controlling the actuation ofthe piston unit.

Changes may loe-made in the speciiication and drawings without departing. fromv the spirit of the inventionv within theseope of the following claims, as set forth.

What I claim is:

l. In a. fluid moto;` comprising a cylindrical housing havingy apistonv unit" adapted to reciprocate therein, saidpiston unitl comprising a plurality of cylindricalmembers arrangedin' spaced relation to each other,` an inlet conduit providing constantly maintained supplyY pressure fluid in communication with the housing, a passageway for directing pressure iiuid to one end'ofthe piston unit to cause actuation thereof in a.. power stroke, a main valve unit disposed in the piston unit for controlling the flow of pressure fluid to the piston, a pilot valve sldably Vdisposedin the main valve and responsive to them'ovement of the piston to controlthe positioning of the main Valve, and springmeans responsive to movement of the piston-to controlthemovementof the pilot valve.

2. In a hydraulic motor comprising. a cylindrical housing having a piston unit adapted to reciprocate therein, means4 providing constantly maintained supply pressure fluid.l iny communication with the housing4 and in constant contact with one face of the piston unit, main valve means disposed in the piston unit for controlling the low of the supply pressure fluid to the opposite facev ofthe piston unit tocause actuation thereof` in a power stroke, a pilot valve slidably disposed in the main lvalve, afvalve rod, therefor, a nut coupling the pilot valve with the rod, said pilot valve maintained in one position by the pressure of the supply uid acting against the rod and nut, a.' helical, spring ca -operating withv the valverod and responsive to movement of the piston unit to, cause' movement" of the pilot valve against the pressure of the supply luidVsaid movement of the pilot valve permitting a positioning of the main valve by the supply fluid pressure to control the now of supply pressurefluid,` tothe lastY mentioned face of the piston.

3. In a hydraulic-power apparatus comprising a housing having a piston unit adapted to( reciprocate therein, means providing constantly maintained supply pressure uidfincommunication with the housingrand` in constant contact with one face.. of ther piston, an automatic`V valve mechanism operable inone direction to direct the supply pressure uid to` an oppositel face of the Piston. Said; Valvefmechanism operable in another position to precludeA supply pressure fluid toV the last mentioned: face Ofthe piston and simultaneously permitting exhaust of theIrv inthe valve mechanisme@ Sprfme means, @of

Operatinsi-Withfthe;pilot valve and. responsive to a movement of the piston for moving the pilot valve to a position to control the position of the valve mechanism.

4. In combination with a hydraulic power unit and a horizontal boring apparatus, a iluid actuated reciprocating piston having an impact cutter connected therewith, an automatic valve mechanism operable in one direction to direct the supply pressure fluid to one end of the piston, said valve mechanism operable in another position to preclude supply pressure fluid to the last mentioned end of the piston and simul taneously permitting exhaust of the supply pressure fluid from the last mentioned end of the piston, a pilot valve slidably disposed in the valve mechanism, said pilot valve maintained in at least one operative position by the supply pressure fluid, and spring means cro-operating with the pilot valve and responsive to a movement of the piston for moving the pilot valve to a position to control the position of the valve mechanism.

5. A fluid motor comprising: a cylinder and a piston unit reciprocable therein and having a rst end face of relatively small eective area and an oppositely directed end face of relatively large effective area, said cylinder having fluid inlet means adapted to provide constant communication between said ilrst end face of the piston unit and a source of operating fluid under pressure; said piston unit having a passage therein adapted, when open, to communicate said oppositely directed end face of said piston unit with the source of operating iluid; main valve means carried by the piston unit and operable by fluid pressure to alternately open and close said passage; and a pilot valve mounted in said main valve means and movable with the piston unit and operable, upon predetermined movement of the piston unit, to control the application of operating fluid pressure to said main valve means to actuate the same.

6. A fluid motor comprising: a cylinder and a piston unit reciprocable therein and having a first end face of relatively small effective area and an oppositely directed end face of relatively large effective area, said cylinder having fluid inlet means adapted to provide constant communication between said first end face of the piston unit and a source of operating uid under pressure; said piston unit including a piston rod having an exhaust passage therein; said piston unit having a rst passage in constant communication with the source of operating fluid and a second passage in constant communication with said exhaust passage; main valve means carried by the piston unit and operable by fluid pressure to provide communication between said oppositely directed end face of the piston unit and, alternately, said iirst passage and said second passage; and a pilot valve mounted in said main valve means and movable with the piston unit and operable, upon predetermined movement of the piston unit, to control the application of operating lluid pressure to said main valve to actuate the same.

7. A fluid motor comprising: a cylinder and a piston unit reciprocable therein and having a nrst end face of relatively small effective area and an oppositely directed end face of relatively large eiective area, said cylinder having fluid inlet means adapted to provide constant communication between said rst end face of the piston unit and a source of operating fluid under pressure; said piston unit including a valve housing carried thereby and main valve means reciprocable in said housing and operable to control the application of operating fluid pressure to said oppositely directed end face of the piston unit, said main valve means having a relatively small pressure area constantly subjected to 0p-g erating fluid pressure and an oppositely directed relatively large pressure area; and a pilot valve carried by and movable with the piston unit and operable, upon predetermined movement of the piston unit, to control the application of operating nuid pressure to said relatively large pressure area of said main valve means.

8. A nuid motor comprising: a cylinder and a piston unit reciprocable therein and having a first end face of relatively small eiective area and an oppositely directed end face of relatively large effective area, said 'cylinder having uid inlet means adapted to provide constant communication between said rst end face of the piston unit and a source of operating i'luid under pressure; said piston unit including'a valve housing carried thereby; main valve means reciprocable in said valve housing in opposite directions to alternately apply and release operating uid pressure to and from said oppositely directed end face of the piston unit; and a pilot valve mounted within and movable with said valve housing, said pilot valve being reciprocable relative to said main Valve means upon predetermined movement of said piston unit and being operable, upon movement thereof in'one direction, to effect movement of said main valve means in the opposite direction.

9. A fluid motor comprising: a cylinder and a piston unit reciprocable therein and having a nrst end face of relatively small e'iective area and an oppositely directed end face of relatively large effective area, said vcylinder having fluid inlet means adapted to provide V constant communication between said rst end face of the piston unit and a source of operating fluid under pressure; main valve means carried by the piston unit and operable by uid Vpressure to control the application of operating flnid pressure to said oppositely directed end face of the piston unit; a pilot valve carried by said main valve means and movable therewith during the major portion of each stroke thereof, saidV pilot valve being movable relative to said main valve means to control the application of operating uid pressure to said main valve means to actuate the same; and actuating means connected to` said pilot valve and engageable with cooperating abutment means associated with Vsaid cylinder to eiect movement of said pilot valveV relative to said piston unit upon predetermined movement of said piston uniti 10. A fluid motor comprising: a cylinder and a differential area piston reciprocable therein and having a relatively small'eiective pressure area and an oppositely directed relatively large effective pressure area, said cylinder having uid inlet means adapted to provide constant communication between said relatively small pressure area and a sourceof operating fluid 'under pressure; a valve housing; main valve means reciprocable in said housing and operable to provide communication between said relatively large pressure area and,V alternately, said source of operating iiuid anda zone of lower pressure than that of the operating fluid to eiect reciprocation of said piston; said main valve means having a relatively small pressure area Yconstantly subjected to operating fluid pressure and'having an foppositely l directed relatively 'large pressure area; and va 4pilot lvalve carriedby and-reciprocable in said valve housing and-operable, upon lpredetermined movement vof said piston, to provide communication between-said relatively large pressure area on saidfmain 'valve fmeans and,

alternately, said source of Aoperating fluid and said zone of lovverlpre'ssure.

1l.. A piston and valve assembly for a fluid motor comprising: a lpiston having a first end face of relatively small :effective area and an tive'thereto to provide Vcom'muni'cationbetween said second passageand, alternately, 'said'rst passage and said third ypassage;and apil'otvalve mounted in saidimainval've'rnieans and operable to control the actuation of said main valve means.

i2. A piston and valve assembly for a fluid' -motor comprising: a piston and a piston rod connected thereto, said piston rod having an exhaust passage therein, saidfpiston havinga first en'dface of relatively small effective area and an oppositely directed end face of relatively large effective area, said piston having a first passage therein communicating with said first end face thereof, a second passage communicating with said oppositely directed end face thereof, and a third passage communicating with said exhaust passage in said piston rod; fluid-actuated main valve means carried by the piston and movable relative thereto to provide communication be- -tv/'een said second passage and, alternately, said first passage and said third passage; and a pilot valve mounted in said main valve means and operable to control the actuation of said main valve means.

13. A piston and valve assembly for a fluid motor comprising: a piston having a first end face of relatively small effective area and an oppositely directed end face of relatively large effective area, said piston having a first passage therein communicating with said first end face thereof, a second passage therein communicating with said oppositely directed end face thereof, and a third passage therein communicating with an exhaust passage; a first valve seat associated with said first passage, and a second valve seat associated with said third passage; a fluidactuated valve member carried by the piston and movable into engagement with said rst seat to close said first passage and provide communication between said second and third passages, said valve member being movable, alternately, into engagement with said second seat to close said third passage and provide communication between said first and second passages; and a pilot valve mounted in said valve member and operable to control the actuation of said valve member.

14. A piston and valve assembly for a fluid motor comprising: a piston having a rst end face of relatively small effective area a'nd an oppositely directed end face of relatively large effective area, said piston having a rst passage therein communicating with said first end face thereof, a second passage therein communicating with said oppositely directed end face thereof, and a third passage therein communicating with lan lexhaust :passage a rfirst valveseat associated engagement with said 'second .se'at 'to lclo'se 'said third passage fand `provide vcommunication between said rst an'dfsecon'd -p'assa'g'es ;v said valve `member' havingoppositely directedpressure areas,

one of' which 4isexposedto said rst passage; said valve memberlhavingiafourth passage communicating at one fend "Withfsaid first passage,

land .having a ffth p'as'sa'ge communicating at ione end lwith said'third pas's'age; and a 'pilot valve --movably-mourited Lin 'sai-d valve member and operableitolpI-ovide` communication between the other of saidf-pressureareas'on v'said valve member Sand, l.alter'natelly, said iourth passage and said fifth passage.-

rl5. A fluid'motor'comprising: ra cylinder and a i piston unit re'ciprocable therein Vand having a first end face of relatively fsmalleffective area tand ian 'oppositelyIdire'ctediendlface of relatively lar-ge effective f area, said ''cylinder having iiuid linlet-means adapted *to provide constant communication between vsaid first lend fface of the piston Lunit' and Sa source fof io'peratin'g fluid under pressure; said piston unit including a valve housing carried thereby, main valve means slidably mounted within said housing and operable by fluid pressure to control the application of operating fluid pressure to said oppositely directed end face of the piston unit, and a pilot valve slidably mounted within said housing and movable with the piston unit, said pilot valve being operable, upon predetermined movement of the piston unit, to control the application ofoperating fluid pressure to said main valve means to 'actuate the same; said pilot valve having a valve rod connected therewith and extending through a wall of said valve housing, said valve rod having abutment means thereon adapted to engage cooperating abutment means associated with said cylinder to move said pilot valve relative to said housing to an intermediate position wherein it is effective to cause actuation of said main valve means by fiuid pressure, said pilot valve being adapted to be moved from said intermediate position to a final position and to be held in said nal position by a fiuid pressure differential between the interior and exterior of said valve housing, established by actuation of said main valve means.

16. A fluid motor comprising: a cylinder and a piston unit reciprocable therein and having a first end face of relatively small effective area and an oppositely directed end face of relatively large effective area, said cylinder having fluid inlet means adapted to provide constant communication between said rst end face of the piston unit and a source of operating iiuid under pressure; said piston unit having a passage therein adapted, when open, to communicate said oppositely directed end face of said piston unit with the source of operating fluid; main valve means carried by the piston unit and operable by fluid pressure to alternately open and close said passage; and a pilot valve carried by said piston unit in coaxial relation to said main valve means and operable, upon predetermined movement of the piston unit, to control the applii5 cation of operating iiuid pressure to said main valve means to actuate the same.

17. A piston and valve assembly for a fluid motor comprising: a piston having a iirs-t end face of relatively small effective area and an oppositely directed end face of relatively large effective area, said piston having a rst passage therein communicating with said rst end face thereof, a second passage therein communicating with said oppositely directed end face thereof, and a third passage therein communicating with an exhaust passage; fluid-actuated main valve means carried by the piston and movable relative thereto to provide communication between said second passage and, alternately, said rst passage and said third passage; and a pilot valve carried by the piston in coaxial relation to said main valve means and operable to control the actuation of said main valve means.

18. A piston and Valve assembly for a fluid motor comprising: a piston having a first end face of relatively small effective area and an oppositely directed end face of relatively large eiective area, said piston having a rst passage therein communicating with said rst end face thereof, a second passage therein communicating with said oppositely directed end face thereof, and a third passage therein communicating with an exhaust passage; and a Valve unit detachably secured to said piston, said valve unit compris- 16 ing a Valve housing, uid-actuated main valv means mounted in said valve housing and operab'le to provide communication between said second passage and, alternately, said rst passage and said third passage, and a pilot valve mounted in said valve housing and operable to control the actuation of said main valve means.

OSCAR E. DEMPSEY.

REFERENCES CITED Y The following references are of record in the file of this patent:

UNTED STATES PATENTS Number Name Date 260,337 Vanduzen June 27, 1882 607,630 Ringbom July 19, 1898 752,491 Warren Feb. 16, 1904 927,560 Lewis July 13, 1909 1,031,340 Howard July 2, 1912 1,254,644 Allen et al. Jan. 29, 1918 2,191,369 Chenault Feb. 20, 1940 FOREIGN PATENTS Number Country Date 24,145 Germany Oct. 29, 1883 17,140 Great Britain Sept. 13, 1895 718 Denmark Sept, 1, 1896 368,750 France Oct. 17, 1906 

